Method of establishing minimum coil annealing time for maximum production

ABSTRACT

A process for determining the minimum length of time to operate an annealing furnace, such as a hood- or bell-type, to anneal a charge of coils of strip metal, some of which may have different sizes or weights, wherein a size factor is established for each coil based on its size and weight and a weight factor is established for the total weight of the charge based on a predetermined temperature to which the charge is to be annealed. The time period for operating the furnace for such a charge of coils is substantially equal to the product of the total weight of the charge, the highest size factor noted, and the weight factor. As a convenient means of quickly determining these factors, families of curves graphically representing prior histories of annealing runs in a given type of furnace are constructed from which the values for the factors are easily and accurately noted and, if necessary, extrapolated.

United Mates Patent Inventor ltohert R. Hill Westlalie, Ohio Appl. No. 9.396

Filed Feb. 9, 1970 Patented Aug. 3, 1971 Assignee lLee Wilson Engineering tlfounpnny, line.

Cleveland, Ohio Continuation-impart of appllication Ser. No. 764L192, Oct. ll, WW, now abandoned.

MllE'lllllUD Oil ESTAHMSHHNG MllNllMUlt/l C'OllL ANNEAMNG Tilt/ll: IFOlll MAl illll/lllllll/ll IPlitOlDIUCTlIUN 14 Claims, 3 Drawing Figs.

Pages 82 and 83 of industrial Furnaces" Volume I, 5th

edition by W. Trinlts and M. H. Mawhinney. Coypright 1961 by John Wiley & Sons. New Yorlt, New York A copy is in Group 344 Primary Examiner-John J. Camby Altorney-Bosworth, Sessions, l-lerrstrom 81 Cain ABSTRACT: A process for determining the minimum length of time to operate an annealing furnace, such as a hoodor bell-type, to anneal a charge of coils of strip metal, some of which may have different sizes or weights, wherein a size factor is established for each coil based on its size and weight and a weight factor is established for the total weight of the charge based on a predetermined temperature to which the charge is to be annealed. The time period for operating the furnace for such a charge of coils is substantially equal to the product of the total weight of the charge, the highest size factor noted, and the weight factor, As a convenient means of quickly determining these factors, families of curves graphically representing prior histories of annealing runs in a given type of furnace are constructed from which the values for the factors are easily and accurately noted and, if necessary, extrapolated.

Patented Aug. 3, 1971 3 Sheets-Sheet 1 FIG. l

ATTORNEYS.

Patented Aug. 3, 1971 3,596,891

FIG 2 .75

m VEN'I m. ROBERT R HILL ATTORNEYS.

MIETIIOID 01F ESTABLISHING MINIMUM COIL ANNEALING TIME FOR MAXIMUM PRODUCTION CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-impart of application Ser. No. 764,192, filed Oct. 1, 1968, now abandoned in the name of Robert R. Hill and entitled Method of Establishing Minimum Coil Annealing Time for Maximum Production.

BACKGROUND OF THE INVENTION Within the past two decades, hoodor bell-type furnaces have come into extensive use for annealing or otherwise heat treating steel, copper, copperalloys, aluminum, and the like, and represent a marked advance over the earlier practice of heating a charge in a box-type furnace. As used here and in the claims, the terms "anneal and annealing" extend to and include any treatment involving heating of a charge which may be carried out in a furnace.

The bell-type of furnace embodies a batch operation, and a considerable period of time is required to raise the temperature of the charge to a desired point. Various means have been employed to shorten the annealing cycle, such as circulation of an atmosphere within an inner or protective cover and, in the case of annealing strip in coils, the use of convectors or spacers between the stacked coils to permit the passage of heated gas over and the absorption of heat through the edges of the coil laps, that is, axially instead of radially.

In spite of such improvements, a difficult problem remains in that, given a predetermined desired annealing temperature, it has previously been difficult to estimate accurately how long an annealing furnace should be operated in order that literally every portion of every coil in a furnace charge reaches this temperature but the last part of the charge to reach annealing temperature is not heated substantially higher than such temperature. Since production schedules for annealed coils rarely if ever permit all coils of a furnace charge to be of the same size and/or weight, the problem is peculiarly accentuated in that coils differing in widths, diameters, or weight often form part of the same charge to be annealed simultaneously in a furnace.

Operators of furnaces today are guided almost wholly by past experience in determining annealing cycles and rely on rulesof-thumb which, again, are based on previous experience. In almost all cases the operators, to be on the safe side, allow much more than enough time to reach annealing temperature in all parts of the charge and employ soak or holding times which are more than sufficient properly to anneal the coils.

Particularly when the coils being annealed are of random widths, diameters, and weights, it is clear that at least some of the coils will be over-annealed, i.e., subjected to higher than the required temperature for longer than the required time, because an annealing cycle is selected to cover the individual coil which is most difficult to anneal. Such over-annealing does not harm the other coils as long as excessively high temperatures are not reached but excessive over-annealing obviously wastes production time of the annealing equipment as well as the considerable amount of fuel used to fire the furnace.

It is, therefore, an object of this invention to provide a procedure for determining an annealing cycle whereby all of the coils in a charge will be acceptably annealed, even though the charge is made up of coils of different widths, diameters, and/or weights, and the most difficult to anneal coil will not be over annealed.

SUMMARY OF THE INVENTION The present invention establishes the minimum length of time required acceptably to anneal, under predetermined conditions, a charge of coils, even though the coils may individually differ from one another in size or weight. In accordance with the present invention, the minimum length of time to operate an annealing furnace for a charge of coils is determined by establishing a size factor, in a manner to be later described, for a coil of the charge based only on its dimensional width and its mass or weight. This size factor is indicative of the annealability of the coil, the larger the factor the longer the annealing time. When, as is almost invariably the case, the coils of a charge are not identical in size and weight such a size factor is similarly determined for each coil. A second factor, hereinafter referred to as the weight factor, is also determined as later described. This weight factor is based only on the weight of the entire charge, the comparative sizes of the coils here being immaterial, and the minimum annealing temperature to be reached throughout the charge.

These factors are based on prior histories of annealing operations for the general type of furnace in which the annealing operations are to be carried out. The numerical values for such factors are derived from families of curves graphically illustrating a correlation between the values mentioned, that is, between the coil width and coil weight for the size factor; and between the total weight of the charge and the minimum annealing temperature for the weight factor.

In any event, the minimum time period required for the annealing operation on a given charge is substantially equal to the product of the highest size factor (where there are coils of different sizes and/or weights), the weight factor, and the total weight of the charge.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical cross-sectional view through a conventional bell-type annealing furnace for metal coils and exemplilies one type of furnace for which the present process may be adapted;

FIG. 2 is a family of curves for deriving the defined size factor and may be designed for use, for example, with the type of furnace illustrated by FIG. I. In this instance, units are taken in the English system and reckoned on coil width in inches and coil weight in pounds; and

FIG. 3 is a family of curves for deriving the defined weight factor and likewise may be designed for use with the type of furnace shown in FIG. ll. English units taken in this instance are the weight of the charge in tons and the annealing temperature in degrees Fahrenheit. The annealing period determined as explained herein by the factors of FIGS. 2 and 3 results in a time value expressed in hours.

DESCRIPTION OF THE PREFERRED EMBODIMENT There are many variables within a furnace, often working in competition with each other, which affect the annealing of coils. The principal variables are:

l. Coil weight 2. Coil width 3. Charge weight 4. Furnace control temperature 5. Work control temperature 6. Soak" or holding period In order to develop a process for determining the minimum annealing time for maximum production in a coil annealing furnace, the effects of these six factors should be accounted for. Thus, as the width of a coil increases it takes longer to heat. In addition, the mass or weight of each coil has a direct effect on the time necessary to bring the entire coil to a desired temperature To minimize Variables l and 2, the approach of the present invention is to classify coils according to their relative ease or difficulty in transferring heat from the outer surface of the coils to the coldest" or most inaccessible point within the coil, sometimes referred to in the art as the center-center of the coil. To account for Variables l and 2 a size factor is derived which, as previously explained, is based only on the width of the coil and its weight. These size factors are preferably graphically illustrated in FIG. 2 wherein a family of curves readily enables the user to establish a size factor,

based on Variables l and 2, for coils to be annealed in furnaces of the type shown in FIG. 1. It is emphasized that this size factor accounts for the coils individually regardless of the diameters of the coils which need not even be measured in the practice of the present invention. The data of FIG. 2 covers coil widths from about 25 inches to about 70 inches and coil weights from about 10,000 pounds to about 60,000 pounds, although values outside these ranges can be extrapolated.

It is understood, of course, that the total weight of the coil charge materially affects the annealing time. For example a 20-ton coil ofa given width would be annealed faster in a 30- ton charge than in a 60 -ton charge. Coupled with this consideration is that of the minimum temperature selected for the annealing.

To take into account variable 3 of the above list weight factors, as previously defined, are derived based on the weight of the entire charge and the annealing temperature which is to be used. Preferably, these weight factors are graphically illustrated as in FIG. 3 wherein a family of curves enables the user readily to establish a weight factor for charges to be annealed in furnaces of the type shown in FIG. 1. The data of FIG. 3 cover charge weights from about 20 tons to about 80 tons and annealing temperatures (at the center-center of the coil) from about ll50 F. to about 1300 F., although values outside these ranges can be extrapolated. The temperature values of FIG. 3 cover the complete range from commercial quality to extra deep drawing quality for steel coils. If desired, separate graphs of the data for deriving the weight factor can be constructed for annealing other types of metal, for example, tin plate.

To assist in the accurate establishment of minimum annealing times for charges of coils of strip in a furnace it is most desirable to reduce substantially, or eliminate, the effects of Variables 4, 5 and 6 on the annealing time. This may be accomplished by control of the temperature of the circulating gas stream in which a control thermocouple is placed in the stream of the circulating gas, as it leaves the diffuser section of the furnace, in such a location that the effect of the radiant heat from the burners, or other heat source, is instantly detected by this thermocouple. The heat source is responsive to this thermocouple so that a known constant temperature is maintained in the convection gases.

Such gas stream temperature control permits the annealing operator accurately to control the outer wrap temperature of the coil so as to eliminate or minimize grain enlargement. Maintaining the gas stream at a given temperature throughout the long cycle protects the coils on the outside against harmful overheating while creating a maximum heat head potential for heating the coil interiors. This brings the center-centers of the coils to temperature faster than if the heat input is gradually reduced as is the case when controlling the temperature by a thermocouple disposed at the bottom center of the bottom coil of the charge as has previously been the common practice.

It has been determined that, in accordance with the present invention, an operator need concern himself with only the following four items to establish the correct annealing cycle time:

I. The minimum annealing temperature sought, that is, the desired temperature at the center-center of the coil, also sometimes referred to as the quality" of the anneal.

2. The size factors for the coils.

3. The total weight ofthe charge.

4. The weight factor, based on item 3.

In order to calculate the number of hours required to anneal a given stack of coils, the operator merely proceeds in accordance with this formula:

S,,,X WXC=H wherein S is the size factor for a coil, S being the largest size factor of all the coils of the charge; W is the weight factor; C is the total weight of the charge in tons; and H is the minimum annealing period in hours. This is the minimum time required to heat to the selected temperature the center-center of the coil most difficult to anneal of those in the charge.

Before giving a working example of the application of the present invention to the determination of the minimum annealing time for a particular furnace charge an explanation will be given of the manner in which the curves of FIGS. 2 and 3 may be derived.

DERIVATION OF CURVES OF FIG. 2

For a furnace charge of four coils, each weighing 25,000 pounds and having a width of 38 inch, the minimum time properly to anneal the coils at 1280 F. is determined from actual data of the operation ofa furnace ofa particular design to be 25 hours. Inserting this time value as the H" in the formula previously noted, assuming a weight factor value W of unity, and inserting at C the total charge weight of 50 tons (4X25,000 pounds), the s factor in the formula calculates out at 0.5. Then, taking a coil width of 38 inch along the abscissa of the graph of FIG. 2, and an S factor of 0.5 along the ordinate, point I is plotted where shown in FIG. 2.

To determine another point on this curve another charge of coils, each having a weight of 25,000 pounds but having a width different from the 38 inch width coils used to determine Point 1, is annealed under the same conditions and the proper annealing time in hours noted. Thus if four 25,000-pound coils (making up a charge of 50 tons), each coil having a width of 55 inch, are annealed at I280 F. and it is found from the furnace operating 'data that a minimum annealing time of 28.6 hours is required, then by substituting these figures in the formula and solving for S," a value of 0.57 is arrived at. A point having an abscissa of55 and an ordinate ofO.57 is then plotted on the graph of FIG. 2 and Point 2 on the 25,000-pound coil curve of FIG. 2 is located.

In like manner, the minimum times properly to anneal other charges of four coils, each coil weighing 25,000 pounds but the coils of each charge being of a different width, is determined from actual furnace operating data and the annealing times inserted at H in the formula, along with the other proper values, and the formula solved for S. By this means a series of points are determined which represent the S factors for 25,000-pound coils of varying widths and, after a reasonable number of points have been plotted, the curve a is drawn therethrough from which the S factor for any 25,000-pound coil of a width from about 22 inch to about 72 inch may be readily determined.

Similarly, the minimum times required to anneal charges of coils of weights different from 25,000 pounds are determined and corresponding curves drawn through the plotted values. For example, the curves b and c are plotted from furnace operating data for coils weighing respectively 35,000 pounds and 45,000 pounds each. By constructing a number of curves in this manner the vertical spacing of the curves is developed and is noted to be substantially directly related to the difference in the coil weights. It is also noted that the curves are substantially parallel. Accordingly, a family of curves as" shown in FIG. 2 may be drawn which enables prompt determination of the S factor for coils weighing from 10,000 pounds to 60,000 pounds and having a width of from about 22 inch to about 72inch.

DERIVATION OF CURVES OF FIG. 3

The curves of FIG. 3 which plot the weight factor against the actual weight 0 of the charge in tons for various annealing temperatures from 1300 F. down to 1 F, are also derived from the previously noted formula S,,,XW C=H and data of actual furnace operation. Thus, point 1 on FIG. 2 (which appears on the 25,000-pound coil curve) may be used to establish Point 1 on FIG. 3, it being known that the weight factor W used in the formula to derive the FIG. 2 curves was unity and that the annealing temperature was l280 F. It was also known that the total charge weight used in establishing Point I on FIG. 2 was 50 tons and, using this charge weight as the abscissa and the weight factor I as the ordinate, Point 1 on FIG. 3 may be plotted.

To establish another point on the I280 IF. curve of FIG. 3 actual furnace operating data is referred to which shows that for a charge of coils having a total weight of 60 tons, the coil of the charge having the highest S factor having such a factor of 0.5, took 27.5 hours (determined from actual furnace opcrating data) for proper annealing at I280 I". Substituting these data in the formula thus 0.5 w l50=27.5 and solving for W gives a value of0.92 and this is used to plot Point 2 of FIG. 3 at an ordinate of 60 and an abscissa of 0.92.

Point 3 on the l280 F. curve of FIG. 3 was determined in a similar manner from actual furnace operating data and additional points, as necessary to enable a proper curve to be plotted therethrough, are determined by use of furnace data and the formula as noted above. When sufficient points are plotted the curve a of FIG. 3 is drawn therethrough.

In the same manner points can be determined and plotted from furnace operating data at other annealing temperatures until a family of curves as illustrated in FIG. 3 is obtained.

The use of these curves in assisting in the determination of the minimum proper coil annealing time for a particular furnace charge will now be explained.

WORKING EXAMPLE I The following disclosure describes one type of annealing furnace for which the present invention is adapted and provides a typical determination of the time for the annealing cycle ofa particular furnace charge.

The invention is especially suited for the type of annealing furnace illustrated in FIG. I of the accompanying drawings. However, adjustments may be made in the factors or manner of constructing the graphs to reflect other types of furnace structures.

A typical bell-type furnace for annealing coils of strip metal is shown in FIG. I. This includes the furnace bell F which is adapted to be positioned over the charge on the furnace base B. As illustrated, the furnace bell F consists of a cylindrical, open bottomed structure which carries a series of combustion heating tubes ll disposed about its inner wall. These tubes are suitably supplied with fuel and air from circular manifolds 3 and 4, respectively, and the products of combustion are discharged through exhaust pipes 5. As is well understood, the bell F is provided with a downwardly projecting sealing flange at its lower edge which projects into a groove or trough 6 in the base B when the bell is in heating position. Sand or other suitable sealing material in the trough 6 provides a seal to prevent undesired flow of atmosphere between the room and the bell.

A charge support and diffuser unit, generally indicated at S, is carried by the base B which almost supports the fan motor 7. The vertical shaft of the motor 7 extends upwardly through the base B and carries the fan or blower 9 at its upper end. This fan is of the usual centrifugal type having a plurality of blades or vanes I0, a bottom plate Ill, and a top plate 12. An inlet opening I3 is formed in the top plate and, when the fan is operating, gas is drawn inwardly through the opening I3 and discharged radially outwardly from the periphery of the fan blades.

The charge support and diffuser S include a baseplate Id, a plurality of spirally extending diffuser vanes l5, and a top plate 16. An outer rim I7 extends around the support at the outer ends ofthe vanes IS. The diameter of the top plate I6 is smaller than the inside diameter of the rim 17 to provide an annular discharge aperture I0 for the gas which is forced outwardly through the diffuser vanes by the fan 9. A central opening 19 in the top plate I6 is provided to permit gas to enter the fan 9.

Three coils C,, C andC are shown, although the charge may contain any practical number. The bottom coil C is supported on the top plate 16 of the charge support S, and a spacer or convector 20 is preferably interposed between the bottom of coil G and the plate I6. Coils C and C, are superimposed on coil C and are spaced from the adjacent coils by convectors or separators which are indicated at 23 and 24. These separators may talte any desired form and are such as to provide a passage for the flow of gas across the end faces of the coils from the outside into the inner opening in the coils, thus greatly facilitating the transfer of heat to the coils.

Disposed over the entire charge is the usual relatively thin sheet metal inner cover fii which is closed at its upper end and provided with a flange portion 26 at its: open lower end. When in operating position, this flange 26 extends into a body of sand or other sealing material in an annular trough 27 in the base B. Means (not shown) are provided for maintaining the desired atmosphere around the charge by directing gas (usually a nonoiridizing gas) into the space within the inner cover and an outlet for such gas is also provided. As is well understood, the space within the inner cover 25 is purged of air before the heating operation is started and the nonoxidizing atmosphere is maintained during the annealing cycle.

The circulation of atmosphere within the inner cover 25 is downwardly through the central openings in the coils C C and C into the fan 9, outwardly through the diffuser unit S, and upwardly through the annular discharge 10 into the space between the outside of the coils and the inside of the inner cover 25. Part of the gas discharged through the opening I8 passes through the convectors 20, 23, and 2d and into the central openings in the coils, while another part moves up and across the top of the top coil C, and downwardly into the central opening thereof.

In a typical run in a furnace of the type described the three coils may be assumed to have these data:

Using the data of the first three columns and the graph of FIG. 2, the coil width of 48 inches of coil C plotted on the abscissa of the graph by the dotted line 3 0 intersects the curve for a weight of 50,000 pounds at a point on the ordinate of the graph as indicated by the dotted line Elli. This results in an S factor for coil C of 0.675. Similarly, the S factors for coils C and C are, respectively, 0.393 and 0.575. Since the S factor for coil C is the largest, it is controlling and therefore used in determining the annealing period.

The total weight of all three coils is 100,000 pounds or 50 tons and the selected minimum annealing temperature is l260 F. The weight factor is determined from FIG. 3 by plotting from its ordinate at 50.0 a horizontal dotted line 32 and, from the point where line 32 intersects the curve for the annealing temperature of 1260 lF., dropping a vertical line 33 to the abscissa of the graph of FIG. 3. This results in a weight factor of 0.965.

The programming time for the annealing run is determined by the previously stated formula, S, W C=H, to be:

The furnace is accordingly operated for 32,6 hours which is sufficient properly to anneal all three coils, regardless of their differences in size and weight.

The present invention may be adapted to process a series of several successive charges in a furnace in the most expeditious and timesaving manner. Rather than selecting a charge of several coils at random from a relatively large supply of differently sized coils to be annealed, in the: preferred practice of the invention an S factor for each coil of'a large group of coils is determined in the manner described. Then each charge to the furnace is made up of a number of coils having the same S factor, or as nearly the same S factor as is possible.

It is pointed out that this step is not merely a visual examination but rather is a classification according to S factors which are indicative of the relative annealability of the several coils, and which correlate coil weight, coil width and the operating characteristics of the furnace being used. For example, assume a supply of nine coils as follows:

In this art it is customary to refer to furnace output in tons per hour of annealed product. Prior to the present invention successive furnace charges and cycle times were established by the operator and the metallurgist largely on the basis of experience. Such procedure is almost invariably wasteful of furnace time because the so determined cycles are set to accommodate the worst condition and ordinarily over-anneal the charge. If, however, the furnace charges are selected on the basis of the S factors of the available coils so that the S factors of the coils making up any one charge are the same, or as nearly the same as possible, the total furnace operating time and fuel consumption may be materially reduced.

To illustrate, the minimum time to anneal at l280 F. a charge consisting of coils l, 2 and 3, is, according to the curves and formula described above:

0.6x l .05 45=28.35 hours Similarly, the minimum time to anneal at l280 F. a charge consisting of coils 4, 5 and 6 is also 28.35 hours; and the minimum time to anneal a charge consisting of coils 7, 8 and 9 is likewise 28.35. The total minimum time to anneal all nine coils in these three charges is therefore 85.05 hours or an annealing rate of 1.59 tons per hour.

In contrast, were the operator to proceed by grouping the nine coils according to their respective S factors and annealing together those having the same or nearly the same S factor, the result is quite different. Thus, the minimum time to anneal coils 1,4 and 7 (each of which has the same S factor of 0.4) at l280 F. is:

0.40X l l 8X37.5=l 7.7 hours Similarly, the minimum time to anneal at l280 F. a charge consisting of coils 2, 5 and 8 (S factor of 0.5 for each) is 23.6 hours; and the minimum time to anneal a charge consisting of coils 3, 6 and 9 (S factor of 0.6 for each) is 30.40 hours. The total minimum time to anneal all nine coils in these three charges is 71.7 hours or 1.88 tons per hour. This results in a reduction of 13.4 hours over the first-described order of annealing the same nine coils and an improvement of 18.2 percent in tons per hour annealed.

Therefore, in accordance with the present invention, to determine the optimum manner in which to anneal a supply of coils of various strip widths and weights in a given annealing furnace, the coils are first preclassified according to their S factors. These S factors may be determined for each coil in the manner previously described and the preclassification may be done at any convenient time.

The so classified coils may then be grouped into charges of suitable total weight, the individual coils of which have S factors which are as nearly the same as possible. These charges are then annealed in the furnace in any order desired. The time period for each successive charge is determined as previously described, i.e., the annealing time in hours being the product of the total weight of the charge in tons, the highest S factor of the several coils of the charge where the S factors are not identical, and the weight factor W as determined from prior histories of annealing in the furnace, such as the curves of FIG. 3.

The present annealing programming method enables an operator to obtain increased production from an annealing furnace as compared with conventional annealing cycle determinations. The present process also lends itself to more efficient utilization of annealing furnaces by classifying coils before they are loaded into a furnace. Coils which differ in size and/or weight, but which actually have the same or substantially the same size factor (FIG. 2), require individually the same annealing time. Such coils can be loaded as part of the same charge to a furnace, thereby eliminating the common wasteful practice of over-annealing some coils in order to satisfy the most demanding conditions. Moreover, when it is necessary to anneal as one charge coils having substantially different individual annealing time requirements, the furnace can be operated in accordance with the present invention so as to reduce to a minimum the unavoidable consumption of fuel and loss of production time of the furnace.

While the foregoing describes a preferred embodiment, it is understood that the invention may be practiced in still other forms within the scope ofthe following claims.

Iclaim:

1. A process for determining the length of time to operate an annealing furnace adapted to anneal a charge of metal coils by reaching a predetermined temperature within a predetermined time, wherein at least two of such coils are of different sizes or weights comprising:

a. determining a size factor for annealing each coil based on its size and weight from a graphical representation of prior histories of annealing in said furnace,

b. determining a weight factor for annealing the total weight of such charge at a desired temperature from a graphical representation of prior histories of annealing in such furnace, and

c. then determining a time period to operate the furnace for such charge of coils that is substantially equal to the product of the total weight of the charge, the highest factor determined in step a, and the factor of step b.

2. The process of claim 1 wherein the factor for step a is determined in accordance with the family of curves of FIG. 2.

3. The process of claim 1 wherein the factor for step b is determined in accordance with the family of curves of FIG. 3.

4. The process of claim 1 wherein the factor for step a is determined in accordance with the family of curves of FIG. 2, and the factor for step b is determined in accordance with the family of curves of FIG. 3.

5. A process for annealing a charge of a plurality of metal coils in a bell type of annealing furnace having circulating atmosphere and adapted to reach a predetermined temperature within a predetermined time, comprising:

a. measuring the width and weight of each coil of the charge and determining a size factor for annealing each such coil based on its size and weight from a graphical representation of prior histories of annealing in such furnace,

b. establishing the total weight of such charge and determining a weight factor for annealing such total weight to a desired temperature from a graphical representation of prior histories of annealing in such furnaces, and

c. then stacking such coils in tiers within the annealing furnace and operating the furnace for a period of time substantially equal to the product of the total weight of the charge, the highest factor determined in step a, and the factor of step b.

6. The process of claim 5 wherein at least two of such coils are of different sizes or weights.

7. The process of claim 5 wherein the temperature of said circulating atmosphere is maintained substantially constant.

8. In a process for annealing a plurality of metal coils in an annealing furnace adapted to reach a predetermined temperature within a predetermined time, wherein at least two of such coils are of different weight or sizes, the steps of insuring that all coils are acceptably annealed regardless of size and weight in a minimum amount of time and without wasting heat energy, comprising:

a. determining a factor for each of such coils in accordance with the family of curves of FIG. 2, based on the width and weight of each coil,

b. determining a factor in accordance with the family of curves of FIG. 3, based on the total weight of all the coils and the minimum annealing temperature to be reached throughout such coils, and

c, then operating the annealing furnace for a period of hours substantially equal to the product of the total weight of all the coils, the highest factor determined in step a, and the factor of step b.

9. The method of operating a furnace for heating coils of strip metal which includes the steps of preclassifying a plurality of coils according to size factors based on the weight and width of the individual coils and the operating characteristics of the type of furnace in which the coils are to be annealed whereby each coil is assigned a numerical size factor, selecting coils to make up successive charges in the furnace which charges are made up of coils having size factors as close to each other as possible from the supply of preclassified coils available, and establishing the annealing time for each charge on the basis of the highest size factor of the coils making up the charge and the operating characteristics of the furnace.

10. A process for annealing a supply of coils, wherein at least some of the coils have different sizes or weights, by treating successive charges of said coils within an annealing furnace including:

a. determining a size factor for each coil based on its size and weight from a graphical representation of prior histories of annealing coils in said furnace,

b. grouping the coils of said supply into furnace charges, the coils of each charge having size factors that are as close to each other as possible,

0. and successively annealing each charge in said furnace for a time sufficient to properly anneal the coil of the charge having the highest size factor.

11. The process of claim lit) wherein the size factor is determined in accordance with the family of curves of FIG. 2,

12. The process of claim 10 including determining a weight factor for annealing the total weight of each of said charges at said predetermined temperature from a graphical representation of prior histories of annealing in said furnace, and then determining a time period for step c for each of said charges that is substantially equal to the product of the total weight of the charge, the greatest S factor for the coils of each charge where the S factors are not identical, and said weight factor for the total weight of the charge.

113. The process of claim 12 wherein the weight factor for the total weight of each charge is determined in accordance with the family of curves of FIG. 3.

114. The process of claim 12 wherein the size factor for each coil of each charge is determined in accordance with the family of curves of FIG, 2, and the weight factor for the total weight of each charge is determined in accordance with the family of curves ofFlG. 3. 

1. A process for determining the length of time to operate an annealing furnace adapted to anneal a charge of metal coils by reaching a predetermined temperature within a predetermined time, wherein at least two of such coils are of different sizes or weights comprising: a. determining a size factor for annealing each coil based on its size and weight from a graphical representation of prior histories of annealing in said furnace, b. determining a weight factor for annealing the total weight of such charge at a desired temperature from a graphical representation of prior histories of annealing in such furnace, and c. then determining a time period to operate the furnace for such charge of coils that is substantially equal to the product of the total weight of the charge, the highest factor determined in step a, and the factor of step b.
 2. The process of claim 1 wherein the factor for step a is determined in accordance with the family of curves of FIG.
 2. 3. The process of claim 1 wherein the factor for step b is determined in accordance with the family of curves of FIG.
 3. 4. The process of claim 1 wherein the factor for step a is determined in accordance with the family of curves of FIG. 2, and the factor for step b is determined in accordance with the family of curves of FIG.
 3. 5. A process for annealing a charge of a plurality of metal coils in a bell type of annealing furnace having circulating atmosphere and adapted to reach a predetermined temperature within a predetermined time, comprising: a. measuring the width and weight of each coil of the charge and determining a size factor for annealing each such coil based on its size and weight from a graphical representation of prior histories of annealing in such furnace, b. establishing the total weight of such charge and determining a weight factor for annealing such total weight to a desired temperature from a graphical representation of prior histories of annealing in such furnaces, and c. then stacking such coils in tiers within the annealing furnace and operating the furnace for a period of time substantially equal to the product of the total weight of the charge, the highest factor determined in step a, and the factor of step b.
 6. The process of claim 5 wherein at least two of such coils are of different sizes or weights.
 7. The process of claim 5 wherein the temperature of said circulating atmosphere is maintained substantially constant.
 8. In a process for annealing a plurality of metal coils in an annealing furnace adapted to reach a predetermined temperature within a predetermined time, wherein at least two of such coils are of different weight or sizes, the steps of insuring that all coils are acceptably annealed regardless of size and weight in a minimum amount of time and without wasting heat energy, comprising: a. determining a factor for each of such coils in accordance with the family of curves of FIG. 2, based on the width and weight of each coil, b. determining a factor in accordance with the family of curves of FIG. 3, based on the total weight of all the coils and the minimum annealing temperature to be reached throughout such coils, and c. then operating the annealing furnace for a period of hours substantially equal to the product of the total weight of all the coils, the highest factor determinEd in step a, and the factor of step b.
 9. The method of operating a furnace for heating coils of strip metal which includes the steps of preclassifying a plurality of coils according to size factors based on the weight and width of the individual coils and the operating characteristics of the type of furnace in which the coils are to be annealed whereby each coil is assigned a numerical size factor, selecting coils to make up successive charges in the furnace which charges are made up of coils having size factors as close to each other as possible from the supply of preclassified coils available, and establishing the annealing time for each charge on the basis of the highest size factor of the coils making up the charge and the operating characteristics of the furnace.
 10. A process for annealing a supply of coils, wherein at least some of the coils have different sizes or weights, by treating successive charges of said coils within an annealing furnace including: a. determining a size factor for each coil based on its size and weight from a graphical representation of prior histories of annealing coils in said furnace, b. grouping the coils of said supply into furnace charges, the coils of each charge having size factors that are as close to each other as possible, c. and successively annealing each charge in said furnace for a time sufficient to properly anneal the coil of the charge having the highest size factor.
 11. The process of claim 10 wherein the size factor is determined in accordance with the family of curves of FIG.
 2. 12. The process of claim 10 including determining a weight factor for annealing the total weight of each of said charges at said predetermined temperature from a graphical representation of prior histories of annealing in said furnace, and then determining a time period for step c for each of said charges that is substantially equal to the product of the total weight of the charge, the greatest S factor for the coils of each charge where the S factors are not identical, and said weight factor for the total weight of the charge.
 13. The process of claim 12 wherein the weight factor for the total weight of each charge is determined in accordance with the family of curves of FIG.
 3. 14. The process of claim 12 wherein the size factor for each coil of each charge is determined in accordance with the family of curves of FIG. 2, and the weight factor for the total weight of each charge is determined in accordance with the family of curves of FIG.
 3. 